Move src/voice to src/audio for better naming

Many of these files are used by Audio and Voice messages.

Fixes https://github.com/vector-im/element-web/issues/18131

src/audio/RecorderWorklet.ts

@@ -0,0 +1,82 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { IAmplitudePayload, ITimingPayload, PayloadEvent, WORKLET_NAME } from "./consts";
+import { percentageOf } from "../utils/numbers";
+
+// from AudioWorkletGlobalScope: https://developer.mozilla.org/en-US/docs/Web/API/AudioWorkletGlobalScope
+declare const currentTime: number;
+// declare const currentFrame: number;
+// declare const sampleRate: number;
+
+// We rate limit here to avoid overloading downstream consumers with amplitude information.
+// The two major consumers are the voice message waveform thumbnail (resampled down to an
+// appropriate length) and the live waveform shown to the user. Effectively, this controls
+// the refresh rate of that live waveform and the number of samples the thumbnail has to
+// work with.
+const TARGET_AMPLITUDE_FREQUENCY = 16; // Hz
+
+function roundTimeToTargetFreq(seconds: number): number {
+    // Epsilon helps avoid floating point rounding issues (1 + 1 = 1.999999, etc)
+    return Math.round((seconds + Number.EPSILON) * TARGET_AMPLITUDE_FREQUENCY) / TARGET_AMPLITUDE_FREQUENCY;
+}
+
+function nextTimeForTargetFreq(roundedSeconds: number): number {
+    // The extra round is just to make sure we cut off any floating point issues
+    return roundTimeToTargetFreq(roundedSeconds + (1 / TARGET_AMPLITUDE_FREQUENCY));
+}
+
+class MxVoiceWorklet extends AudioWorkletProcessor {
+    private nextAmplitudeSecond = 0;
+    private amplitudeIndex = 0;
+
+    process(inputs, outputs, parameters) {
+        const currentSecond = roundTimeToTargetFreq(currentTime);
+        if (currentSecond === this.nextAmplitudeSecond) {
+            // We're expecting exactly one mono input source, so just grab the very first frame of
+            // samples for the analysis.
+            const monoChan = inputs[0][0];
+
+            // The amplitude of the frame's samples is effectively the loudness of the frame. This
+            // translates into a bar which can be rendered as part of the whole recording clip's
+            // waveform.
+            //
+            // We translate the amplitude down to 0-1 for sanity's sake.
+            const minVal = Math.min(...monoChan);
+            const maxVal = Math.max(...monoChan);
+            const amplitude = percentageOf(maxVal, -1, 1) - percentageOf(minVal, -1, 1);
+
+            this.port.postMessage(<IAmplitudePayload>{
+                ev: PayloadEvent.AmplitudeMark,
+                amplitude: amplitude,
+                forIndex: this.amplitudeIndex++,
+            });
+            this.nextAmplitudeSecond = nextTimeForTargetFreq(currentSecond);
+        }
+
+        // We mostly use this worklet to fire regular clock updates through to components
+        this.port.postMessage(<ITimingPayload>{ ev: PayloadEvent.Timekeep, timeSeconds: currentTime });
+
+        // We're supposed to return false when we're "done" with the audio clip, but seeing as
+        // we are acting as a passive processor we are never truly "done". The browser will clean
+        // us up when it is done with us.
+        return true;
+    }
+}
+
+registerProcessor(WORKLET_NAME, MxVoiceWorklet);
+
+export default null; // to appease module loaders (we never use the export)